Many different types of exercising machines currently in use are provided with one or more exercising levers operatively connected to a resistance force in the form of a weight stack. The user can vary the amount of resistance force applied to the exercising lever by varying the number of weights operatively connected to the exercising lever. However, the weight stack used in this type of exercising machine is expensive to produce and the weights increase the overall weight of the exercising machine.
Also, the resistance force applied by the weights connected to the exercising lever produces the same amount of resistance force in all angular positions of movement of the exercising lever so that the resistance force is applied in a uniform manner throughout the full range of movement of the exercising lever. Thus, the maximum resistance force which can be applied by the weights is limited to the maximum amount of resistance force which can be overcome by the weakest position of the particular muscles being exercised by the user. With this type of uniform resistance, the weakest position of the muscle receives the maximum amount of exercise while the strongest position of the muscle receives a minimum amount of exercise and the muscle is not worked to its capacity.
In order to overcome this limitation, a group of different types of exercising machines has been developed in which a variable radius cam is interposed between the weight stack and the exercising lever so that "full range" exercise of the muscles is obtained. In this type of exercise machine, the amount of resistance force being applied in various positions of the exercising lever is varied so that the muscles of the user are subjected to the proper amount of resistance force in all positions of movement to provide a much more effective "full range" exercising program. Examples of this type of exercising machine are disclosed in U.S. Pat. Nos. 3,858,873; 4,387,893; and 4,456,245.
It is also known to provide exercising machines with the resistance force being provided by elastic cords or springs, such as for example the exercising devices disclosed in U.S. Pat. Nos. 1,750,549; 1,866,868; and 3,770,267. However, these exercising devices still provide a substantially uniform resistance force throughout at least the middle range of movement of the muscles of the user. Also, it is difficult for the user to accurately and properly adjust the amount of resistance force applied by the elastic cords or springs in this type of machine.
Exercising machines have also been provided with resistance force in the form of hydraulic valves, cylinders or pistons and the like. Examples of exercising machines of this type are illustrated in U.S. Pat. Nos. 3,529,474; 3,784,194; and 3,848,467. Exercising machines have also been provided with resistance force in the form of brake devices in which a brake shoe is pressed against a rotating disk, as for example the exercising machine disclosed in U.S. Pat. No. 3,074,716. However, these types of exercising machines also apply a uniform resistance force to the exercising lever in all positions of movement of the lever so that these types of exercising machines do not provide the most efficient "full range" exercise. Also, the hydraulic valves, cylinders or pistons, as well as the brake devices, are expensive and it is difficult for the user to adjust these devices to provide the proper amount of resistance force to be imparted to the exercising lever.